CRISPR/cas9 endonuclease-mediated homology-directed repair was used to replace a portion of exon 7 with the orthologous human PAH sequence surrounding and containing an amino acid substitution at position 281 altering proline to leucine (P281L; c.842 C to T) of the phenylalanine hydroxylase (Pah) gene on chromosome 10. (J:344273)